The invention relates to an internal axes single-rotation machine, whose external and internal rotors are rotatable about parallel geometrical axes running through the centre of gravity thereof with a uniform angular velocity differing in an integral ratio, the surfaces bounding the engagement spaces of the external rotor in the circumferential direction in the inwards direction form a widening adjacent to an outer region radial thereto with parallel surfaces or surfaces forming a widening in the outwards direction, the engagement spaces in the axial direction being bounded by surfaces of side walls at right angles to the axis.
Numerous different constructions of such machines are known. A machine with a speed ratio between the external and internal rotor of 2:1 is e.g. known from U.S. Pat. No. 4,540,356. Machines in which this speed ratio is 3:2 and 4:3 are described in the not previously published U.S. Pat. No. 4,714,417. As a result of the mounting of their two rotors about axes passing through the centre of gravity thereof, such machines are suitable for very high rotational speeds, so that in the case of small dimensions they can be realized for a high drive throughput. However, the pressure level attainable when used as a compressor is greatly dependent on the precision of manufacture. Furthermore, the efficiency when used as a machine driven by a gas flow, i.e. as a driver is dependent on the precision of manufacture or the accuracy of the reciprocal engagement of the rotors. Therefore it has not hitherto proved possible to manufacture machines of the aforementioned type with satisfactory performance characteristics as a mass product, i.e. at an acceptable cost. The engagement spaces of the external rotor having undercuts made it necessary to assemble the external rotor from separately manufactured components, so that on joining together the components dimensional inaccuracies were unavoidable, as was a correspondingly large clearance between the external and internal rotors. However, when not using packing strips, the clearance at the engagement points between the two rotors, i.e. the size of the sealing gap present thereat is decisive for the attainable machine ouput.